This invention relates to a water heater, and is more particularly directed to a type of water heater having a main burner for heating a heat exchanger and a standing burner. It also has a main fuel passage for supplying fuel to the main burner, the main fuel passage having a manual valve which is adapted to be opened by a manual operation member and an automatic valve downstream from said manual valve which is adapted to be opened in conjunction with a water pressure sensitive member in response to water being supplied to the heat exchanger. Also provided is a standing burner passage for supplying fuel to the standing burner, the standing burner passage branches out from the main fuel passage at a point between the two valves.
It is generally, desirable with this type of water heater that the manual operation member be inoperable when the heat exchanger is supplied with water. Because the automatic valve is opened when water is supplied to the heat exchanger, if the manual valve is then opened by the manual operation member, a large amount of unburned gas is discharged from the main burner, thus creating the possibility of an explosion if an ignition device is operated.
As a water heater of this kind which is free from the foregoing inconveniences, a well known example is shown in FIG. 1. For instance, if a manual operation member a is operated by pushing, a manual valve b constituting a safety valve is opened and at the same time a changeover switch c is changed over from the left to the right, that is, from its normally closed contact point side to its normally opened contact point side. Thus, ignition device d, is ignited causing a standing burner e to be ignited. If, after the completion of this ignition operation, a heat exchanger f is supplied with water, the changeover switch c is changed over by its own return spring (not illustrated) to its normally closed contact point side, and at the same time a detecting switch is closed by a water pressure sensitive member g in response to a supply of water to the heat exchanger, an electromagnetic type automatic valve is then energized and opened resulting in main burner j being ignited. (See Japanese Utility Model Pulbication No. Sho 50-6034). Thus, this type of apparatus is advantageous so that even though the detecting switch h is closed to open the automatic valve i when water is supplied to the heat exchanger, if the manual operation memmber a is then operated, the changeover switch c is changed over to its normally open contact point side, thereby causing the automatic valve i to be deenergized and closes becoming inoperative. Therefore, even if the manual valve b is then opened, the main burner j is not supplied with gas. Thus, the foregoing inconveniences can be eleminated.
This type however, is inconvenient in that the changeover switch c is liable to have a contact fusion problem caused by heat.
If, accordingly, the contacts of the changeover switch c are fused together in the normally closed position, when the heat exchanger is being supplied with water, and the manual operation member a is depressed, the automatic vlave i remains in its open condition, and as a result there is a danger that a large amount of unburned gas is discharged from the main burner j when the manual valve b is opened. Additionally, if, under this gas discharging condition, the operation member a is pushed with enough force that the contacts of changeover switch c are separated there is a dangerous possibility of an explosion of the unburned gas.